RALEIGH, N.C. — Even hippos and whales, it turns out, can get fat. But how can you tell, let alone slim one down?
Obesity among zoo animals is such a complex problem that zoo nutritionists, scientists and others, from as far away as England, gathered at North Carolina State University on Friday for a two-day symposium on such weighty matters as how to tell when an oyster's weight is about right.
"It's actually a huge problem, and a multifaceted one," said Michael Stoskopf, a professor at the college. "You have to look at not only diets themselves and the amount of calories delivered, but also things like exercise."
The basic cause of chubbiness is no different for moray eels and wildebeests than for humans: "If the energy going in exceeds the energy going out, you're going to get fat," said Karen Lisi, a nutritionist at the Smithsonian National Zoological Park. "We don't like to hear that, but that's pretty much how it is for us, too."
With so much variation among creatures, though, nutritionists have to treat the diet of each species almost like an individual scientific study, determining what it eats in the wild and how best to approximate it in captivity, said Richard Bergl, curator of conservation and research at the North Carolina Zoological Park in Asheboro.
"It's not just a matter of throwing a bucket of apples in with the monkeys and a bale of hay to the elephant," Bergl said.
When your zoo has hundreds of creatures as different as tree frogs, fish, birds and elephants, the task can be overwhelming.
Even among birds, the variation in diet is huge, including hummingbirds that sip nectar, fruit-eating parrots and vultures that chow down on rotted meat. The diet for individual animals may have to be adjusted to compensate for changes such as pregnancy, lactation or simply aging, Lisi said.
Her zoo, with about 400 species and 2,000 individual animals, has its own nutrition lab.
Even simply determining whether an animal is overweight is so complex that part of the symposium was dedicated solely to that topic. Sometimes it's obvious when an animal is morbidly obese, Lisi said. Other times, though, a quirk of a given species, such as thick fur, makes it more difficult, and zoo staff might not be able to tell without tranquilizing it and checking by hand.
Bergl of the North Carolina Zoo is an expert on a rare kind of lowland gorilla and spoke on gorilla nutrition Friday. Captive gorillas can get fat for reasons similar to the boom in human obesity, he said in an interview. Humans haven't evolved to handle the huge amount of calories and fat that many are now eating. Similarly, Gorillas in the wild live on a bulky, low-calorie diet of such things as leaves, shoots and bark, but in zoos are often fed specially formulated "biscuits."
The biscuits give them proper nutrition, but aren't bulky and don't take long to eat, making overeating easy. That also means that zoo gorillas — who spend much of the day foraging in the wild — have little to do, except sit around and look bored, the gorilla equivalent of hanging out on the sofa watching TV all day.
Bergl spoke about four gorillas at the zoo that have been on a no-biscuit diet heavy in vegetables such as kale, cabbage and carrots for a few months. For some of the gorillas, this meant a change from about 30 pounds of high-calorie food a day to more than 100 pounds of low-calorie chow.
It's too early to evaluate the health aspects, but their behavior has improved, he said. They're more active now, and no longer sit around with blank expressions.
This is good not only for the gorillas, Bergl said, but also visitors to the zoo, who get a chance to see gorillas acting more normally.
"You do worry about the psychological well-being of the animals," he said. "But also from the public's standpoint, when people see animals sitting around looking bored, it's hard to empathize with them."
With a spectacled bear that the Smithsonian acquired back in January, the weight problem was obvious. Spectacled bears are agile tree-dwellers in their native South America, but this one was so chubby it struggle just to stand up.
The zoo staff made him a special project, trying to get his weight down before Washington's oppressive summer weather. They modified his diet to reduce the calories, among other things carefully weighing the food. Once he lost some of the weight, he began to do a better job of regulating his own intake, even leaving food uneaten. By August he had slimmed down from about 480 pounds to about 370.
One of that bear's problem before the zoo acquired it, Stoskopf said, was one that's common for animals housed by themselves. Without other animals to interact with, they might get less exercise and develop behaviors like pacing back and forth. Keepers may try to break up those behaviors with treats, but that can simply reinforce it, leading to another round of treats.
A better solution, she said, can be encouraging activities unrelated to eating, such as giving an animal cardboard boxes to rip apart.
There may be lessons in all this for humans, Lisi joked, including acting more like insects, which even in captivity don't seem to have many problems with overeating.
"They're way smarter than us," Lisi said. "They just eat what they need and move on."